Research And Implementation Of Signal Coding Optimization System For Underwater Imaging Sonar

Underwater imaging sonar technology is widely used in exploration of military,submarine landform, inland lakes and rivers, the system is mainly based on the imaging of the acoustic sensor. However, due to its low frequency, narrow bandwidth,and the large number of array elements, there are some problems arising in array-based underwater imaging system such as low frame rate and poor real-time ability. Therefore, the transmit-receive scheme which uses a transmitting array to simultaneously transmit orthogonal signals while a receiving array is adopted to receive echo signals has been used. The target of the paper is to research the system's transmitting signal. In this paper two kinds of orthogonal signals have been designed which are good for the separation of channels, they could overcome the problem due to the large number of arrays and the poor correlation between the signals. It has the characteristics of strong anti-jamming and large bandwidth. These two methods are easy to implement and it is helpful to improve the resolution of underwater imaging.Finally, the actual signals are tested through the hardware circuit and the host computer. And the underwater echo datas are collected and received successfully.Firstly, by introducing the pulse compression signal, the importance of the large time bandwidth signal in signal performance is highlighted. The composite chaotic map system is generated by using the random-like property of chaos and the sensitivity of initial value, it generates a set of pseudo-random sequences and they are used to modulate the phase of the traditional signals. The simulation results show that the composite coded signal has good autocorrelation and cross-correlation and it can effectively separate the signals from the echoes. Compared with the traditional signal optimization method, it is easy to implement and has good performance.Then, an optimal design of frequency hopping binary phase coded signal based on m sequence is introduced. The frequency hopping signal has the characteristics of strong anti-interference, low bit error rate and anti multipath effect in the field of communication, which meets the design requirements of underwater sonar imaging signal. In this paper, we design a frequency hopping binary coded signal based on the good correlation of the m sequence in the frequency range of underwater imaging. The carrier frequency and phase of the signal are transformed in a certain ranges, it has the advantages of frequency modulation and phase modulation, it can also complement each other, the orthogonality and secrecy of the signal under water are improved.Finally, this paper introduces the basic components of underwater imaging system. The function and design of each module of the system are described in detail and the design is verified by experiments. The system consists of main control module,power amplifier module, USB communication module, receiving circuit module and so on,and through the C++ host computer display control terminal design,this paper describes the design of transceiver interface and the communication with hardware,the echo is displayed on the interface through the acquisition of echo data and data communication with the lower computer through USB, it realizes the function of data transmission and preservation.